Hi, I have been trying to implement some basic CSD functionality into openbsc. V.110 transparent mode, to be specific, since this should be the most simple to implement. At first I tried with a nanobts, but that didn't seem to work at all. Now I am using a bs-11. The two phones I use establish a connection, but they cannot exchange data and what I see on the Abis link also doesn't really make sense to me. (Needless to say everything works as expected when using the same phones on a production network.) I attached a pcap of a CSD call I made via the bs-11. The second attachment is the raw dump of the traffic frames I received from the BS-11 for _one_ of the phones. (It looks pretty much the same for the other phone.) The first idle data frames received look ok: 00000000 00 00 c5 ff ff ff ff ff fd ff ff ff ff ff ff ff 00000010 ff fd ff ff ff ff ff ff ff ff fd ff ff ff ff ff 00000020 ff ff ff fd ff ff ff ff C bits (Uplink data), D bits (all set to "1" == idle) and E bits (9.6 kbit/s) are all set as expected. But after the synchronisation phase, things start to get strange. The idle frames suddenly look like this: 00000460 00 00 8a ff ff fe fe fe fa fe fe fe fe fe fe fe 00000470 fe fa ff fe fe fe fe fe fe fe fa ff fe fe fe fe 00000480 fe fe fe fa ff fe fe fe The BTS "forgets" to set the first bit of every octet to "1" on most (but not all) octets. Also, the C bits now state that this is a 14.5kbit/s data frame. The E bits say the user rate now is 7.2 kbit/s. There are only four frames with actual payload data in the dump. These frames are at the positions I expect them to be (40600, 60520, 80440, 100400 - they were sent in intervals of 10 seconds). They look like this: 00009e90 00 00 8a ff 2b a2 fa aa 00009ea0 fa 86 02 22 22 6e fe 1a 26 fa d7 4e d6 52 36 56 00009eb0 4e d6 fa 53 36 56 4e d6 52 36 56 fa 4f d6 52 36 What has been sent by the phone is an eight byte timestamp followed by 22 bytes of 0xaa. But I only get one data frame for each of these transmissions (30 bytes of payload don't fit into one data frame), and if I parse it as V.110 data, I get these 20 bytes: 00000000 15 7d 0d 10 d5 ff 33 fb ae f5 ff ae ba ef fd ba 00000010 ef ae ba ff So no 0xaa bytes there... Does anybody have any idea what I might be doing wrong here? Thanks, -Tobias